Move toolset to the dev16.0p2 compiler

This version of the build task can run correctly on .NET Core 3.0. Our
current one is suffering from a private reflection bug that causes the
build tasks to crash on startup. This is the PR which previously fixed
that bug.

https://github.com/dotnet/roslyn/pull/31763

eng/Versions.props

@@ -73,10 +73,10 @@
     <MicrosoftInternalVisualStudioShellInterop140DesignTimeVersion>14.3.25407-alpha</MicrosoftInternalVisualStudioShellInterop140DesignTimeVersion>
     <MicrosoftMetadataVisualizerVersion>1.0.0-beta1-63011-01</MicrosoftMetadataVisualizerVersion>
     <MicrosoftMSXMLVersion>8.0.0.0-alpha</MicrosoftMSXMLVersion>
-    <MicrosoftNetCompilersVersion>2.9.0-beta7-63018-03</MicrosoftNetCompilersVersion>
+    <MicrosoftNetCompilersVersion>3.0.0-beta2-19068-12</MicrosoftNetCompilersVersion>
     <MicrosoftNetCoreAnalyzersVersion>$(RoslynDiagnosticsNugetPackageVersion)</MicrosoftNetCoreAnalyzersVersion>
     <MicrosoftNetCoreILAsmVersion>2.0.0</MicrosoftNetCoreILAsmVersion>
-    <MicrosoftNETCoreCompilersVersion>2.9.0-beta7-63018-03</MicrosoftNETCoreCompilersVersion>
+    <MicrosoftNETCoreCompilersVersion>3.0.0-beta2-19068-12</MicrosoftNETCoreCompilersVersion>
     <MicrosoftNETCorePlatformsVersion>2.1.0</MicrosoftNETCorePlatformsVersion>
     <MicrosoftNETCoreRuntimeCoreCLRVersion>2.0.0</MicrosoftNETCoreRuntimeCoreCLRVersion>
      <!-- Using a private build of Microsoft.Net.Test.SDK to work around issue https://github.com/Microsoft/vstest/issues/1764 -->